Foams consist of two phases, an aqueous phase and a gaseous (air) phase, so fluid foam is therefore a substance which is formed by trapping many gas bubbles in a fluid structure. Producing a fluid foam involves not only the generation of these gas bubbles, but also the packing and the retention of these bubbles into the overall fluid structure in order to provide a stable foam.
When foaming a fluid, the main difficulties to be faced are to produce the foam desired in a controlled and repeatable way and also to stabilize the foam and to keep it stable for a given period of time.
Devices for foaming milk are known in the state of the art, wherein the foaming of the milk is typically carried out by a rotating part moving inside a reservoir or container where milk is arranged. Typically, this rotating part is configured as a whisk which is provided at the bottom part of the container. Milk foaming occurs by agitation of the milk which in turn traps air inside the liquid film. However, the problem with these known devices is that a precise control and regulation of the characteristics of the foam obtained is very hard to achieve, and repeatability of the process becomes a primary issue.
Also, the state of the art includes devices that inject hot steam into milk that is filled into a container, in order to cause foaming. However, a precise control of the foaming process followed, and repeatability is typically an issue in these known devices.
Also, in the state of the art devices, there are several factors that influence the foaming of the milk as, for example, the speed of the rotating part or the temperature and/or pressure of the steam that is injected into the milk.
Moreover, in the mixing and/or foaming devices known in the prior art the outlet is typically always maintained open, and the mixture delivered in the cup does not have the same characteristics throughout the process: in fact, either a more liquid foam (not stable) or a not properly mixed composition is delivered at the beginning and later, either a thicker (and more stable foam) or a better mixed composition is delivered afterwards. In case of foaming devices, typically the foam remaining in the container is too thick to be delivered through the outlet in most of the cases, which presents a strong hygienic problem and therefore requires frequent cleaning of the container and of the complete device.
Therefore, the present invention is directed to a device for foaming a fluid, preferably for foaming milk, having a controlled outlet that is operable as a function of certain parameters, in order to avoid the drawbacks of the known prior art.